Hydrofoil system



Dec. 15, 1959 v. sc 2,917,016

HYDROFOIL SYSTEM Filed Feb. 25, 1957 2 Sheets-Sheet 1 INVENTOR. fiauus v. SM I Unite HY DROFOIL SYSTEM Harms V. Schertel, Wiesbaden, Germany Application February 25, 1957, Serial N 0. 641,890

Claims priority, application Switzerland April 16, 1951 16 Claims. (Cl. 114-66.5)

States Patent tips which emerge from the water surface at cruising speeds of the craft. The hydrofoil systems according to the known art have a number of serious disadvantages. The longitudinal stability in case of a bow-heavy trim is low, so that the craft will tend to undercut in a high sea if the center of gravity is displaced toward the bow.

Particularly when the aft foil under the action of the emerged foil portions tends to follow the water surface contour, and is raised, the angle of attack and the lift acting on the fore foil are decreased in a wave trough so that the craft tends to undercut in the next approaching wave crest. Furthermore, the draught varies greatly with the speed so that the hull is immersed at only slightly lowered speeds, but will rise too far above the water level at high speeds whereby the stability of the craft will be endangered.

It is one object of the present invention to overcome the disadvantages of the known hydrofoil systems, and to provide a hydrofoil system in which the fore foil tends to follow the water surface and determines the draught of the craft, whereas the aft fo-il tends to maintain the trim position by following the vertical movements of the fore foil.

This means, in other words, that the fore foil according to the present invention changes its lifting force upon small immersion paths and has a low sensitivity against variation of the angle of attack whereas the aft foil is not substantially influenced by the water surface but is more sensitive to variation of the angle of attack.

A craft provided with such a hydrofoil system tends to oscillate parallel to itself and to traverse the waves at small pitching angles. The craft leaves the wave crests without any substantial bow-heavy inclination. Upon increase of the load the craft has a stern-heavy trim for increasing the angle of attack and thereby the hydrodynamic lifting forces acting on the craft.

It is another object of the present invention to provide a hydrofoil system which produces a constant immersion of the fore foil at all speeds of the craft.

With these objects in view, the present invention mainly consists in a hydroplane craft which comprises, in combination, a hull; a fore foil and an aft foil extending transverse to the hull and being secured to the fore and aft portions, respectively, of the hull so as to be loaded with parts of the Weight of the craft and producing a hydrodynamic lifting force acting on the hull for raising the hull upon increase of the speed of the craft until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the shape of at least the fore foil changing from a given fore foil section located below the Waterline toward the hull for increasing the lifting force of the fore foil with respect to the lifting force of the aft foil upon deeper immersion at slower speeds of the craft.

In the preferred embodiment of the present invention, the fore foil and the aft foil have, respectively, a pair of lateral foil portions which are transversely inclined in opposite directions for producing a hydrodynamic lifting force acting on the hull. The shape of the lateral inclined foil portions changes from the sections which are located below the waterline of maximum speed toward the hull in such a manner that the hydrodynamic lifting force produced by the fore foil is always greater than the hydrodynamic lifting force produced by the aft foil, and moreover that the difference between the lifting force of the fore foil and the lifting force of the aft foil increases upon deeper immersion at slower speeds of the craft.

The tips of the fore foil are preferably secured to the hull, and the tips of the aft foil are spaced from the hull so that at selected speeds, the aft foil is completely submerged. According to one embodiment of the present invention, the aft foil is completely submerged even at the maximum speed of the craft.

The submerged aft foil portion has a higher aspect ratio S /A and a smaller lift coefiicient C than the portion of the fore foil which is submerged at maximum speed of the craft.

In order to produce an increasing lifting force of the fore foil with respect to the lifting force of the aft foil upon deeper immersion as occurring when the speed of the craft is reduced below maximum speed, the chord, the mean line of camber and the angle of attack of the inclined lateral fore foil portions increases with respect to the aft foil from the fore foil sections which are located below the water surface at maximum speed of the craft toward the tips of the fore foil and toward the hull, such that the difference in size between said three features of the fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil section, is the greater the further away they are located from this section. In the preferred embodiment of the present invention the said foil section is located below the waterline of maximum speed at a distance equalling the chord of the foil at said waterline. Of course, it is not necessary to provide all the three above-described features, since any one of these features is sufficient to produce the desired result in accordance with the present invention. It is particularly advantageous to provide bafile plates on the undersides of the lateral inclined foil portions of the fore foil, and to construct the aft foils in such a manner that the lateral portions of same have a greater transverse inclination than the corresponding lateral foil portions of said fore foil and that a submerged center portion is provided with a dihedral angle greater than The preferred embodiment provides a straight center portion.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a side elevation of a hydroplane craft in accordance with the present invention;

aetaoie Fig. 2 is a cross sectional view taken on line 2--2 in Fig. 1;

Fig. 2a is a plan view of the fore foil shown in Fig. 2 with the hull omitted for the sake of clarity;

Fig. 3 is a cross sectional view corresponding to the section of Fig. 2 but illustrating a modified embodiment of a fore foil according to the present invention;

Fig. 3a is a plan view showing the fore foil illustrated in Fig. 3 with the'hull of the craft omitted for the sake of clarity;

Fig. 4 is a cross sectional view taken on line 4--4 in Fig. 1'; i Fig. 4a is a plan view of an aft foil according to the present invention;

Fig. 4b is a plan view of a modified aft foil;

Fig. 4c is a plan view of another modified aft foil;

Fig. 5 is a cross sectional view corresponding to the showing of Fig. 4 but illustrating a modified construction of the aft foil;

' Fig. 5a is a plan view of the aft foil illustrated in Fig. 5;

Fig. 6 is a cross sectional view corresponding to the showing of Fig. 4 but illustrating a modified aft foil;

Fig. 6a is a plan view of the aft foil illustrated in Fig. 6;

Fig. 7 is a cross sectional view illustrating a modified fore foil according to the present invention;

Figs. 8a, 8b, and 8c are, respectively, sectional views taken on lines 8a-8a, 8b8b, and 8c8c in Fig. 2;

Figs. 9a and 9b are sectional views taken on lines 9a9a and 9b9b in Fig. 4, respectively;

Fig. '10 is a diagram illustrating the variations of the lifting forces at different speeds and immersions; and

Fig. 11 is a diagram illustrating thevariations of the lifting forces with the trim angle of the craft.

Referring now to the drawings, and more particularly to Fig. 1, the hydroplane craft comprises a hull 1 having a fore portion 1a and a rear portion 1b. The fore portion In has a gliding surface 2 at the bottom thereof, and the aft portion 1b has a tapering bottom surface 2 which produces no hydrodynamic lifting force upon immersion. The fore portion 1a of the hull supports a fore foil 3, and the aft portion of the hull supports an aft foil 4. The foils 3 and 4 are spaced from each other and are located forwardly and rearwardly, respectively, of the center of gravity of the craft which is placed substantially midships so that each of the foils rear and fore is loaded with a part of the weight and load of the craft.

Fig. 2 illustrates one embodiment of a fore foil which includes two opposite lateral portions 30. Each lateral inclined portion 30 includes an upwardly and outwardly inclined part 31 and an inwardly and upwardly inclined part 32, parts 31 and '32 being connected by vertical portion 33.

At maximum speed of the craft the hull and the upper portions of the fore foil will rise until the foil sections 34 are located at the surface level of the water. Such surface level of the water is indicated by the line WL. When the speed is reduced, the surface of the water will be positioned at the line a, and when the speed is further reduced the surface of the water will be located at the line b.

The modified embodiment of the fore foil shown in Fig. 3, has lateral inclined portions similar to the embodiment of Fig. 2 but the inwardly and upwardly inclined part 32 of inverted V-shape reaches further down. The positions of the fore foil shown in Fig. 3 with respect to the water surface is again indicated by the line WL, a and b. From the plan views of Figs. 2a and 3a it is apparent that the longitudinal chord of the emergent foil portions 31 increases from section 8c, which is located somewhat below WL, toward the juncture portion 33, and that the chord of part 32 increases toward the hull. Consequently the lifting force produced by the fore foils according to the present invention increases at a higher rate upon deeper immersion of the fore foil as occurs when the speed of the craft is reduced below maximum speed than by a rectangular foil. The emergent portions of the fore foils are shaped in such a manner that the sections located closer to the hull are capable of pro ducing a greater lifting force .upon immersion than the sections located farther spaced from the hull. In the embodiment of Figs. 2 and 2a, the lower ends of foil portions 32, and foil portions 33 have the same width, and are narrower than the upper ends of foil portions 31 which project from portions 33 at the juncture with the same.

Figs. 4, 5 and 6, and the associated Figs. 4a, 4b, 40, 5a, and 6a illustrate several embodiments of aft foils according to the present invention. The shape of the alt foils is somewhat different from the shape of the fore foils. While the fore foils extend up to the hull, the aft foils 4 are connected by struts 5 to the hull 1.

In the embodiment of Figs. 4 and 4a, the aft foil has two opposite lateral portions 41 which are inclined to the longitudinal plane of symmetry of the craft and to the water surface and extend upwardly and outwardly. A center portion 45 connects the lateral portions 41. At maximum speed of the craft a section 44 of the lateral portions 41 will be located at the surface level WL of' the water. A section located somewhat below WL is shown in Fig. 9b. When the speed of the craft is reduced, the water surface will be located in the horizontal plane a, and upon further reduction of the speed will be located at the horizontal plane b. It will be noted that the horizontal plane b is located above the upper ends of foil portions 41 while portions 31 of the fore foil are still immersed in this position of the craft. A comparison of the constructions shown in Figs. 4, 5 and 6 will prove that the lateral inclined portions 41 are of difierent lengths so that in the embodiment of Fig. 4 portions of the aft foil will emerge at all speeds exceeding take off speed, whereas in the embodiment of Fig. 5 the aft foil will be submerged when the speed drops under the maximum speed. In the embodiment of Fig. 6, the aft foil will be completely submerged at all speeds of the craft, even at the maximum speed.

A comparison of the plan views of Figs. 2a and 3a with Figs. 4a, 4b, 40, 5a and 6a will prove that the area of each emergent fore foil portion is substantially greater than the area of the associated aft foil portion. More particularly the emergent inclined lateral portions of the fore foil have agreater increase in length of chord than the inclined lateral portions of the aft foil. The chord 20 at section 34 is shorter than the chord 21 of the fore foil. The chord 50 is shorter than the chord 51 of the aft foil. It will be understood that the chords 2t) and 50 are simultaneously located on the water surface at top speed, whereas the chords 51 and 21 are located at a water surface at a reduced cruising speed. In accordance with the present invention the increase in length between the chord 20 and the chord 21 is greater than the increase in length between the chord 5t) and the chord Sll. Consequently the lifting forces produced by the fore foil increase at a higher rate than the lifting forces produced by the aft foil upon deeper immersion and vice versa. Equal increase of lifting forces is obtained with a smaller immersion path at the fore foil.

When the chord of the aft foil is constant as shown in Fig. 4b, the difference between the lifting force of the fore foil and the lifting force of the aft foil increases to an even greater extent. When the chord of the aft foil is reduced in outward direction as shown in Fig. 4c the difierence between the lifting forces produced in differently immersed positions of the fore foil and aft foil increases to an even greater extent.

In the event that the aft foil is shaped as shown in Fig. 4c, it is possible to provide a fore foil whose chord is constant since in all positions of the craft, the chord of the emergent fore foil portion-will be longer than the chord of the aft foil, and the difference between the respective associated chords will increase upon deeper immersion.

. The same is true with regard to the aft foil constructions shown in Figs. 6, 6a, which produce no increasing lifting forces upon deeper immersion so that in this event the greatest possible increase of lifting forces is obtained by the fore foil compared with the aft foil.

In the aft foil construction shown in Figs. 5 and 5a, the ends of the lateral portions 41 widen for the purpose of more fully utilizing the surface effect. The surface effect reduces the sub-pressure on the top side of the foil near the water level, and this effect diminishes when the spacing of this part from the water level increases so that an additional stabilizing force is produced.

As explained above, the lifting force produced by the fore foil increases to a greater extent upon deeper immersion than the lifting force of the aft foil. This effect cannot only be obtained by the increase of the length of the chord above the foil section 8c which is located below the water surface at maximum speed, but can also be obtained by other constructive features. A higher lifting force of the foil sections which are located above the foil section 80 can also be obtained by varying the profile of the emrgent foil portions 31. As shown in Figs. 8a, 8b, and 8c, the mean line of the camber of the profile increases from the foil section 8c towards the tips of the fore foil or toward the hull. The camber of mean line of the foil section 8a shown in Fig. 8a is greater than the camber of mean line of the foil section 8b shown in Fig. 8b and this mean line of camber again is greater than the mean line of camber of the foil section 8c shown in Fig. 80. Consequently the profile of the fore foil is such that the higher sections of the fore foil are capable of producting a greater hydrodynamic lifting force than the lower sections of the fore foil. In accordance with the present invention, the increase of the lifting force obtained by the portion of the fore foil located between the fore foil section 8c and the highest fore foil section, increases at a higher rate than the lifting force produced by corresponding aft foil sections shown in Figs. 9b and 9a which have a constant camber of mean line and are located in corresponding horizontal planes.

A third way of obtaining the desired results of the present invention is to increase the angle of attack of the portions 31 from section 30 in upward direction so that a greater lifting force is produced upon deeper im mersion of the fore foil when the speed is reduced below maximum speed. As shown in Figs. 8a, 8b and 8c, the angle of attack of the fore foil portions 31 increases from foil section 8c toward the hull. The angle of attack a. of the fore foil section 8a is greater than the angle of attack at of the foil section shown in Fig. 8b, and angle a is again greater than the angle of attack of the foil section 8c. The angle of attack of the aft foil portions 41 preferably remains constant as shown in Figs. 9a and 912 so that the difference between the lifting force of the fore foil and the lifting force of the aft foil increases upon deeper immersion of the foils. However, in the event that the aft foil has an increasing angle of attack, the rate of increase of the angle of attack of the fore foil must be greater in accordance with the present invention so that the difference between the lifting force of the fore foil and the lifting force of the aft foil increases when the foils are immersed deeper than section 34 when the speed of the craft is reduced below maximum speed. Furthermore, a greater increase of the lifting force on the fore foil than on the aft foil can be obtained by giving the inclined lateral fore foil portions 31 a smaller transverse inclination with respect to a horizontal plane and to the water level than the inclination of the corresponding aft foil portions.

The diagram of Fig. 10 illustrates the lifting forces 1.; and L At the speed C the immersion of the foils is assumed to be WL. When the speed of the craft is reduced to a speed 0 the surface of the water will be located at the higher level a with respect to the craft, under the presumption that the craft immerses on an even keel.

As clearily shown in Fig. 10 atthe immersion a the hydrodynamic lifting force L; of the fore foil is not only greater than the hydrodynamic lifting force L, of the aft foil, but also the difference D between the two forces is increased as compared with the diflierence D present at maximum speed. If the speed is further reduced, the difference will become even greater as is clearly apparent from the diagram of Fig. 10. Since lifting forces must counterbalance the load placed on the foil the increasing lifting force being effective on the fore foil will cause the same to rise above the presumed level which results in a stern-heavy trim of the craft.

As explained above, such increase of the difierence between the hydrodynamic lifting force of the fore foil and of the aft foil can be obtained by several constructive measures, which may be individually applied, or which may be all applied together to achieve the desired effect of the present invention. At maximum speed the sections 34 of the fore foil are located at the level of the water surface, and the portion of the fore foil between the sections 34- is submerged. Similarly, at maximum speed the portion of the aft foil located between the sections 44 is submerged.

As can be seen from the drawings the submerged portion of the aft foil has a higher aspect ratio as compared with the fore foil which results in a higher lift gradient of the aft foil with respect to the fore foil. In other words the lifting forces of the aft foil increase at a higher rate with the angle of attack, or respectively, with the angle of trim than the lifting forces of fore foil. Furthermore the submerged portion of the aft foil has a smaller lift coefiicient C than the fore foil. Consequently the ratio of lift gradient to lift coefficient dC CL is also increased which gives to the aft foil 2. considerably greater sensitivity to variations of the angle of attack with respect to the fore foil. As a particular embodiment of the invention a high aspect ratio of the aft foil is obtained by the provision of a transverse lengths of the submerged portion of the said foil greater than the transverse lengths of the fore foil as shown in Figs. 4 and 2. Furthermore an increase of lift gradient is obtained on the. aft foil by a smaller mean transverse inclination of the submerged aft foil portion as compared with the corresponding portion of the fore foil. Due to the provision of the horizontal or slightly dihedral, portion 45 on the aft foil, the mean transverse inclination of the aft foil portion which is submerged is smaller than the transverse inclination of the corresponding submerged fore foil portion as shown in Fig. 2. The illustrated aft foils have a mean transverse inclination not greater than the fore foil, even when a greater transverse angle of inclination is provided for the lateral inclined portions of the aft foil, which is favorable for the effects of the present invention. In the embodiment shown in Fig. 6 in which the aft foil remains fully submerged at all speeds of the craft, transversely inclined lateral portions are provided in order to prevent too close an approach to the water surface, for example in a high sea, since an entirely horizontal surface would result in an inrush of air.

In diagram Fig. 11 lifting force L is plotted against trim angle 7' of the craft, which varies identicallywith the angle of attack of the two foils. It is: clearly appar ent from the diagram that the lift forces produced by the aft foil vary to a greater extent with the change of trim aim-tiers than the lifting forces ofthe forefoil. 7., indicates the:

normalt'riin position of the craft.

its draught, thus-following the vertical movement'of the fore foil and tending to restore normal trim position. With a stern heavy trim lifting forces of the aft foil are stronglyfincreased and cause a restoring moment in the inverse sense.

' Accordingto the present invention the fore foil, which changes its lifting force upon small immersion paths and has a lowsensitivity against'variation of the angle of attack tends to follow the water surface whereastne aft foil being moresensitive to such variations of the angle of attack butless influencedby variations of immersion tends to maintain the craft in trim position.

It is obvious that a high longitudinal stability is obtained in the event of a stern-heavy trim,.since at the aftfoil'b'oth load'and angle of attack are increased, whereas. on the other hand thestability with a bow-heavy trim moment'which on the fore foil'increases load and diminishes angle of attack offers severe problems. Due to the hydrofoil system accordingto the inventionlongitudinal stability ofthe craft is considerably improved ascomp'jaredwith the known art. In the eventof bow-heavy moments, the aft foil, being'sensitive to variations of the angle of attack but less sensitive'to variations of immersion, follows the verticalmovement of the fore foil and'increases its draught together with the fore foil, resulting in a substantially smaller negative inclination of the longitudinal'axisof the craft, whereas the heavy loaded fore foil, being less sensitive to variations of the angle of attack but more sensitive to variations of immersion, will; have an increase of lifting forces by the immergingfoil'area higher than the loss of lift by the slightdecrease ofangle of attack. It must be taken into consideration thatbow-heavy stability is lost if the fore foilTlift-reduction, resulting from a decrease of angle of attack,.exceeds lift'increase which results from the augmentation ofemergedfoil area upon deepening immersions. A craft suppliedwith the fully submergedaft foils as shown in Fig. 6, where no influence of water level occurs, attains the highest bow-heavy stability.

. With thedescribed-foil system the craft will have the following performance:

Due to the fact that the fore foil extends up to thegliding surfaces 2 of the hull, an increasing lifting forcev is produced untilfull immersion of the craft, whereas the lift-increase at the aft foil is restricted to a water line spaced-at a distance from the hull. Therefore, on starting,.the lifting force actingon the large immerged area of .the fore foil raises the foreship from the water even at low speeds. The craft trims stern-heavy while the-foils angle of attack increases. When speed reaches a suflicient height the aft foil comes to the water surface as well until the craft runs on an even keel at cruising speed.

In theevent of speed changes, the lifting force on the aft foil is. balanced with greater immersion paths than on. the fore foil so that the craft is automatically trimmedin sucha way that the angle of attack is increasedat decreasing speeds, and is decreased at increasing speeds. The immersion differences of the craft are thus decreased so far that under certain conditions a-constant immersion of the fore foil at all speeds may be obtained. An increase in the load causes a sternheavy trim whereby the angle of attack and consequently; the lifting forceis increased. In.the event of vertical; oscillations of the crafts. center of gravity, the craft responds with an. inclination of its longitudinal axis vwhich produces counteracting balancing forces.

From: the-preceding it is evident that in a sea-way thefore: foil. follows: the. contour of. longer waves, whereas:..the:aft foil .tendsto maintain the trim position sot th 'atnhe .craft-transverses.the-waves at small pitching,

angles.

If. the craft' leaves: its trim positionina bow-heavy sense the aft foil will suffer a heavier loss of'lift than the fore foil' andlincrease' of thefore foil to agreat extent also-hasthe advantage that when the lift and the immersion of" the fore foil are controlled, the'immersion of the aft'foil is also simultaneously controlled. Therefore, means for varyingthe" lifting force, suchv as an adjustment of the angle of attack, are only applied to'the fore foil.

Fig. 7 schematically illustrates the section of a rnodi fiedfore foil whichis mounted in the center of pressure to pivot about an axis 8. The foil isicontrolled by the fin or bafiie'itl to swing into the direction'of' flow so that upon variation of the direction of flow, themag nitude of the lifting force remains invariable; insteadof controlling the. angle of attack of the entire fore foil; flaps'may be provided on the trailing edge of the'fore foil which are controlled by fin 10, if necessarythrough" a lever transmission. For such an arrangement, the fore foil is rendered entirely insensitive'to a variation of the angle of attack whcreby the influence of suchj'a" variation is eliminated and the longitudinal stabilityis increased.

In the embodiment of'Fig; 2, plates'll are'provided on the under side of'the lateral foilportions 31 which extend parallel to the longitudinal axis of' the craft at substantially right angles to the' foil surface. These" plates, when emerged, prevent a' pressure compensation toward the water surface and'thereby increase the'over-' pressure forces on the under side, so that the fore foil tends to follow the water level to an even greater ex tent.

In accordance with the principle of the present inven- 'tion according to which the fore elements tend to follow" the water level while lifting forces on the aft foil are limited, as a particular embodimentof the invention, the fore foil is connected with the hull-by transverselyin=-- clined struts 36 in Fig. 2 which are provided with lift producing profiles, whilstthe struts 5 in Figs. 46, connecting the aft foil with the hull, are provided with lift producing profiles at the most on the portions 51 located adjacent the foil and are otherwise symmetrically profiled without any lifting action. Furthermore the fore part of the craft is provided with gliding planes 2, whereas the. aft portion of the craft is formed to have no dynamic lifting effect. Therefore, the aft portion of the ship tapers rearwardly and is of negative inclination. The aft portion ofthe craft can also be built in round-bottom'shape as shown in Fig. 6. The hullis so formed that the lifting force on the fore portion of the-hull increases at a higher rate than that of the aft portionof the hull when immersion is increased. Suchliftingforce increase is obtained not only'by the length of the-- fore portion of the craft which is progressively Wetted as the immersion increases, but also in a known manner by outwardly sloping fore portion side walls as shown in Figs. 2 and 3, as compared with the side walls of the aft portion of the craft which are vertical or inward-'- ly inclined as shown in Figs. 4-6. Consequently the! craft trims stern-heavy when immersion increases,that is when the load increases, while the angle of attackof the foil is increased.

It will be understood that each of the elementsdescribed above, or two or more together, may also find a useful application in other types of hydrofoil systems differing from the typesidescribedlabove.

While the invention'hasbeen. illustrated and described as embodied in a hydrofoil system including a'fore foiland a rear foil andin which the fore foil increasesits lifting force withrespect to the lifting force of theaft foil upon deeper immersion. of the fore foil at slower. speed of. thecraft, ,it..is not intended. to-be. limited :to the. details shown, since various modifications andlstruc-- turalchanges may be made without departing in any II way from the spirit of the present invention. Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions for producing a hydrodynamic lifting force acting on said hull for raising said hull until at a given maximum speed a pair of corresponding fore foil sections of said lateral foil portions of said fore foil which are spaced given distances from said hull are adapted to be located on the water surface, the shape of said lateral foil portions of at least one of said foils changing along the length of the same for increasing the difference between the lifting force of said fore foil and the lifting force of said aft foil upon deeper immersion of said foils at slower speeds of the craft.

2. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and

producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull, and struts connecting the tips of said aft foil portions to the hull.

3. In a hydroplane craft, in combination, a hull, a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, re spectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft toil being spaced from the hull,

the submerged portion of said aft foil located below said waterline of maximum speed having a higher aspect ratio and a smaller lift coefficient than the submerged portion of said fore foil located between said fore foil sections, and struts connecting the tips of said aft foil portions to said hull.

4. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord of the said lateral aft foil portions,

such that the difference in length of said chord of said fore foil portions and the chord of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull. 5. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the camber of mean line of said lateral foil portions of said fore foil increasing from said fore foil section towards said hull with respect to the camber of mean line of the said lateral aft foil portions, such that the difference in camber of said fore foil portions and the camber of mean line of the respective aft foil portions, spaced at equal distances from. said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull.

6. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions,

- respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the angle of attack of said lateral foil portions of said fore foil increasing from said fore foil section towards said hull with respect to the angle of attack of the said lateral aft foil portions, such that the difference of said angle of attack of said fore foil portions and angle of attack of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull.

7. A hydroplane craft as set forth in claim 6 wherein the chord of said lateral foil portions of said aft foil are of constant length.

an ers '11 weight of the craft, each of saidfoils having'a pair of transversely inclined'lateral foil portions, and producing ahydrodyna'mic lifting force for raising saidhullu-ntil at a given maximum speed a given waterline or" maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect'to the chord, the camber of mean line and the angle of attack ofthesaid lateral aft foil portions, such that the difference in' size between said three features of said fore foil.

portions and the features of the respective aft foil portions', spaced at equal distances from said foil sections, isthe greater the further away they are located from said sections,- sa'id lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull, the submerged portion of said aft foil located below said waterline ofmaximum speed being longer than the submerged portion of said fore foil located between said fore" foil sections, and struts connecting the tips of said aft foil portions to said hull.

9. In a hydroplane craft, in combination, a hull; a fine foil and an aft foil extending transverse to said hull and being'sec'ur'ed to the fore and aft portions, respectively, of said hull. so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing ahydrodynamic lifting force for raising said hull until at a' given maximum speed a given waterline of maximum foilemergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack-of said lateral foil portions of said fore foil increasing from a fore foil section located belowsaid waterline towards said hull with respect to thechord, the camber of mean line and the angle of attack of the said-lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending upto the said-hull, the tips of said lateral foil portions of said aft foil being spaced from the hull, said lateral foil portions of said aft foil having greater transverse inclination than the corresponding lateral foil portions of said fore foil and the submerged portion of said aft foil located below said waterline of maximum speed having a center portion with a dihedral angle greater than 150, and struts connecting the tips of said aft foil portions to said hull.

10. in a hydroplane craft, in combination, a hull; a'

fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the Weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a'hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore'foil and said aft foil is reached, the chord, the camber of mean line ofprofile andthe angle of attack-of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord, thecamber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference-in size'between-said three features-of said fore foil pcrtionsandthe features of the respective aft foil portions, spaced at equal distances from'said'foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foilex-tendingsup to thesaid 'hull, the tipsof said'lateral foil portions of -said-aftfoil being spaced from the hull, each of said lateral foil portions of said fore foil in- 12 eluding anoiitwardly and upwardly inclined inner po'r tion, and an inwardly and upwardly inclined outer por tion, and struts connecting the tips of said aft foil poi tions to said hull.

ll. In a hydroplane craft, in combination, a hullj a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, re: spectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of' transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull untilata given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said" between said three features of said fore foil portions and the features of the respective aft foil portions, spacedat equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of'said aft foil being spaced from the hull, each of said lateral foil portions of said aft foil including an outwardly and up wardly inclined inner portion, and an inwardly and upwardly inclined outer portion being of shorter length than said inner portion, and struts connecting the tips of said aft foil portions to said hull.

12. In a hydroplane craft, in combination, a hull; a1 fore foil and an aft foil extending transverse to said hull' and being secured to the fore and aft portions, respec{ tively, of said hull so as to be loaded with parts of thei weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing, a hydrodynamic lifting force for raising said hull until at a. given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profilef and the angle of attack of said lateral foil portions 0t said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to,

the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the ditference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil; sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull, said aft foil having a lateral portion protruding from; said foil section to such a small extent that said aft foil} is completely submerged at reduced speed, the submerged portion of said aft foil located below said waterline ofmaximum speed having a higher aspect ratio and a smaller lift coefiicient than the submerged portion of;

said fore foil locatedbetween said fore foil sections, and; struts connecting the tips of said aft foil portions to said hull.

13. In a'hydroplane craft, in combination, a'hull; a; fore foil and an aft foil extending transverse to said hull" and being secured to the fore and aft portions, respec tively, of said hull so as to be loaded with parts of the", weight'ofthe craft, each of said foils having a pair of= transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until-= at a given maximum speed a given waterline of rnaxiniun'l-- foil emergence'on said fore foil and'said' aft foil is reached, the cho'rd,.the camber of mean line of'profile and the angle of'attack'of said lateral foil-portions'of said fore foil'increasingfrom-a fore foil section -locatd below said waterline towards said hull with respect to the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sec tions, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull, bafile plates attached to the undersides of said lateral foil portions of said fore foil and extending substantially normal thereto and parallel to the longitudinal axis of said hull, and struts connecting the tips of said aft foil portions to said hull.

14. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said fore foil being provided with auxiliary means adjustable for varying the lift force, said means being provided with a tail plane to direct said means in the direction of flow, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull; and struts connecting the tips of said aft foil portions to the hull.

15. In a hydroplane craft, in combination, a hull; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lateral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, transversely inclined struts connecting said lateral fore foil portions with said hull and having lift producing profiles, and struts connecting said aft foil with said hull having lift producing profiles at the most only at a portion of the struts located adjacent the foil, said lateral foil portion of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull.

16. In a hydroplane craft, in combination, a hull including a fore portion having a bottom gliding surface for producing a hydrodynamic lift force and an aft portion tapering toward the rear so as to produce no hydrodynamic lifting force; a fore foil and an aft foil extending transverse to said hull and being secured to the fore and aft portions, respectively, of said hull so as to be loaded with parts of the weight of the craft, each of said foils having a pair of transversely inclined lat eral foil portions, and producing a hydrodynamic lifting force for raising said hull until at a given maximum speed a given waterline of maximum foil emergence on said fore foil and said aft foil is reached, the chord, the camber of mean line of profile and the angle of attack of said lateral foil portions of said fore foil increasing from a fore foil section located below said waterline towards said hull with respect to the chord, the camber of mean line and the angle of attack of the said lateral aft foil portions, such that the difference in size between said three features of said fore foil portions and the features of the respective aft foil portions, spaced at equal distances from said foil sections, is the greater the further away they are located from said sections, said lateral foil portions of said fore foil extending up to the said hull, the tips of said lateral foil portions of said aft foil being spaced from the hull, and struts conmeeting the tips of said aft foil portions to the hull.

References Cited in the file of this patent UNITED STATES PATENTS 1,976,046 Tietjens Oct. 9, 1934 2,257,406 Von Brutenbach Sept. 30, 1941 2,597,048 Almqvist May 20, 1952 2,767,678 Vertens Oct. 23, 1956 FOREIGN PATENTS 582,985 Great Britain Dec. 4, 1946 OTHER REFERENCES Ser. No. 268,421, Tietjens (A.P.C.), published May 

